The present invention relates to a hydroelectric turbine system and, more specifically, to a new low head or ultra low-head hydropower turbine system.
Water turbines that are best suited for hydroelectric power generation with proven efficiencies and established technological advancement are generally categorized into three groups, (1) Pelton wheels, which are impulse turbines of low specific speed and used for very high head applications, (2) the Francis turbine, which is categorized as a reaction turbine of medium specific speed for medium to high head applications, and (3) the propeller or Kaplan turbines, reaction turbines of high specific speed for low head application. Of these categories, only the propeller or Kaplan turbines would be considered for ultra low-head hydroelectric applications.
A fixed blade propeller turbine has an efficiency curve which decreases sharply for both increasing and decreasing flow and load conditions. This is due to the generation of hydraulic shock resulting from the change of the angle of the relative velocity as flow of the fluid enters the runner and/or the runner speed deviates from that of designed conditions. This makes the application of a fixed-blade propeller turbine unfavorable for fluctuating head conditions unless, of course, modifications are made. To eliminate this disadvantageous feature, changes have been made in the design by allowing the blade pitch to vary in response to the varying flow conditions. These design changes greatly improved the applicability of a propeller turbine under fluctuating flow conditions and load requirements and allowed the propeller turbine to operate at near peak efficiency under a wide range of water head conditions.
However, although the modifications discussed above have been found suitable to some degree in meeting the requirements of changing flow conditions in the related hydroelectric power generation systems, they are not without their disadvantages. For example, the mechanism used to adjust the pitch of the turbine blade is complex and very costly and, thus, for less demanding low head and ultra low-head hydroelectric applications, where a large runner diameter is likely needed, the use of the above-defined modified turbines is not considered economically feasible. In case of micro-hydropower generation, the high cost of the blade pitch adjustment mechanism produces a capital investment problem. In order to extract energy from the vastly available ultra low-head hydroelectric resources, new hydroelectric power generation systems are needed to improve the turbine design and system application so as to economically utilize these resources.